A known method of preparing beverages, in particular coffee, involves the use of different liquid pressures for different kinds of beverages. In particular for coffee machines, it is known to prepare espresso with high liquid pressure and brewed coffee with low liquid pressure.
FIG. 1 shows a coffee machine 1 according to the state of the art. The coffee machine 1 comprises at its input side a pressure reducer D1, which places an upper limit, for example 2 bar, on the input pressure. At the output side of the pressure reducer D1 is a branch point, at which the water flowing in through the pressure reducer D1 can be directed towards a first beverage region for the preparation of coffee and/or towards a second beverage region for the preparation of hot water. In the second beverage region steam can also be produced, for example in order to heat beverages already available outside the apparatus. In the second beverage region are disposed, in sequence in the direction of flow, a nonreturn valve R3 followed by a boiler valve Y2, which can be controlled by an electronic controller E1, and finally a water boiler K in which hot water can be prepared. At the output side of the water boiler K is a hot-water valve Y4, likewise controllable by the electronic controller E1, by way of which the hot water can be released into a vessel, for example the cup shown in the figure.
In the first beverage region a pressure pump M1 is provided at the entrance. Arranged in parallel with the pressure pump M1 is a nonreturn valve R1, to limit the output-sided pressure of the pressure pump M1 to a specified maximum, in particular 8 bar. At the-output side of the pressure pump M1, in sequence in the direction of flow, are first a flow meter B4, then a nonreturn valve R2 and a water heater HW to warm the water needed for the preparation of coffee. At the output side of the heater HW are a first and a second pipe branch, both of which open into a coffee preparation unit KB. In the first pipe branch is an infusion valve Y1, which is controllable by the electronic controller E1, and a flow resistance D2 by means of which the water pressure is made lower at the output side of the second pipe branch than at the input side of the first pipe branch. The infusion valve Y1 is opened when brewed coffee is to be prepared in the coffee preparation unit KB. In this case the pressure pump M1 is turned off, so that water flows through it with no increase in the water pressure. During the preparation of brewed coffee, therefore, only the pressure prevailing in the pipeline at the input side of the coffee machine 1 is used, in particular about 2 bar.
In order to prepare espresso, cafe-creme and similar coffee under pressure, an admixture valve Y3 in the second pipe branch at the output of the water boiler HW is opened. At the same time the pressure pump M1 is operated in such a way that at its output a high liquid pressure is provided, in particular at least 8 bar. Therefore at the output of the second pipe branch, for the preparation of pressurized coffee, a high liquid pressure is available, only slightly below the liquid pressure at the output of the pressure pump M1.
In the preparation of both brewed and pressurized coffee the finished coffee is conducted into a vessel, such as a cup, at the output of the first beverage region.
As described above, the preparation of beverages with the coffee machine 1 depends on an adequate input pressure, in particular at least 2 bar. The pressure pump M1 for the preparation of pressurized coffee is also designed for a corresponding input pressure, if necessary reduced to the specified level by the pressure reducer D1. If the input pressure were lower, in some circumstances the pressure-raising action of the pressure pump M1 would not suffice to generate the required pressure in the second pipe branch and in the coffee preparation unit KB. Furthermore, the preparation of hot water in the second beverage region also depends on an adequate input pressure. The controller of the second beverage region is set to a predetermined input pressure, so that according to the selected mode of operation the right result is obtained, namely either hot water or steam.
If the pressure in the pipes of a water-supply mains system is sufficient, the coffee machine 1 can be connected directly to the water mains. However, if the available water mains do not provide sufficient pipeline pressure, it is possible to interpose external pressure-raising equipment ahead of the coffee machine 1.
FIG. 1 illustrates another case, in which the water for the preparation of beverages in the coffee machine 1 comes from a water tank 3. For this purpose an external pressure-generating apparatus 2 is provided, which by means of a feed pump M2 conveys water out of the water tank 3 and generates a specified minimal water pressure, in particular at least 2 bar, at the output of the pressure-generating apparatus 2. To regulate this minimal pressure a pressure regulator P is provided, which cooperates with the controller E2 of the pressure-generating apparatus 2. The controller E2, in addition to cooperating with the pressure regulator P, actuates a magnetic valve Y5 disposed between the water tank 3 and the feed pump M2. The magnetic valve Y5 also functions as a nonreturn valve, to prevent water from flowing back into the tank 3. This arrangement makes it possible to operate the feed pump M2 only when necessary, i.e. when the pressure at the output side of the pressure-generating apparatus 2 falls below the specified minimum or when water is drawn from the pressure-generating apparatus 2.
When needed, water flows out of the pressure-generating apparatus 2 into the coffee machine 1 and/or into other devices, e.g. accessories of the coffee machine 1 such as chocolate-drink devices or hot-water devices, indicated by "n".